The present invention relates to assays for the assessment of unoccupied binding sites on proteins in biological fluids such as thyroxine binding proteins in serum or plasma samples.
Thyroxine (T4) is a hormone produced by the thyroid gland which is essential for growth and development. In blood more than 99% of the total T4 present is bound to serum proteins, mainly TBG. When assaying for T4 it is necessary to ascertain the total T4 content of the sample and how much free T4 is present as well. Uptake tests for thyroid function have been known for many years. Generally, this test, which is commonly referred to as a thyroid hormone binding assay, provides an assessment of the degree of unsaturation of the protein binding sites, primarily that of TBG, by thyroid hormones and is an indirect index of the patient's thyroid status. The tests typically involve the partitioning of labeled T3 or T4 conjugate between serum and a secondary binder which is a function of the binding sites on the thyroid binding proteins which are free of T4.
Many of these tests require a separation step to separate the secondary binder from TBG. The tests typically require the addition of an external reagent.
It is desirable to have an integral uptake test for thyroid function which does not require the addition of external reagents.